Cosmetic oil thickener and oil-soluble copolymer

ABSTRACT

The invention provides a novel oil thickener that can impart a thickening effect for oils used in cosmetics, and a novel oil-soluble copolymer that can be used as the thickener.The cosmetic oil thickener of the invention is an oil-soluble copolymer having a monomer unit composed of a hydrophilic monomer, a monomer unit composed of an easily-crystallizing hydrophobic monomer, and a monomer unit composed of a poorly-crystallizing hydrophobic monomer.

FIELD

The present invention relates to a novel cosmetic oil thickener, and toa novel oil-soluble copolymer that can be used as the thickener.

BACKGROUND

In the field of cosmetics, it has been attempted to improve the ease ofuse of cosmetics by adding additives such as thickeners and gellingagents to the oils that are used.

PTL 1 discloses an oily liquid thickener for a transparent cosmetic,comprising polyamide-8, and a liquid higher fatty acid having a C12-C22branched or unsaturated alkyl group or a liquid higher alcohol having aC12-C22 branched or unsaturated alkyl group.

PTL 2 discloses an oily thickener for a cosmetic comprising a specificsiliconized polysaccharide compound and a silicone emulsifier.

PTL 3 discloses an oily gelling agent for a cosmetic that includes acopolymer composed of a specific hydrophobic monomer and a specifichydrophilic monomer.

CITATION LIST Patent Literature

[PTL 1] Japanese Unexamined Patent Publication No. 2016-210711

[PTL 2] Japanese Unexamined Patent Publication No. 2014-218468

[PTL 3] International Patent Publication No. WO2016/098456

SUMMARY Technical Problem

Various oils have been used in the field of cosmetics, and this has ledto demand for novel oil thickeners capable of providing a thickeningeffect for the oils.

It is therefore a main object of the present invention to provide anovel oil thickener that can impart a thickening effect for oils used incosmetics, and a novel oil-soluble copolymer that can be used as thethickener.

Solution to Problem <Aspect 1>

A cosmetic oil thickener which is an oil-soluble copolymer having amonomer unit composed of a hydrophilic monomer, a monomer unit composedof an easily-crystallizing hydrophobic monomer, and a monomer unitcomposed of a poorly-crystallizing hydrophobic monomer.

<Aspect 2>

The thickener according to aspect 1, wherein the easily-crystallizinghydrophobic monomer is a monomer of 8 or more carbon atoms that is asolid at ordinary temperature, and the poorly-crystallizing hydrophobicmonomer is a monomer of 8 or more carbon atoms that is a liquid atordinary temperature.

<Aspect 3>

The thickener according to aspect 1 or 2, wherein the hydrophilicmonomer is at least one monomer selected from among the followingformula 1 and formula 2:

where,

R¹ is a hydrogen atom, a glyceryl group, a straight-chain or branchedhydroxyalkyl group of 1 to 4 carbon atoms, or a polypropyleneglycolgroup represented by —(C₃H₆O)_(n)H where n is an integer of 2 to 10, and

R² is a hydrogen atom or a methyl group,

where,

R³ is a hydrogen atom or a methyl group, and

R⁴ is a straight-chain or branched alkyl or hydroxyalkyl group of 1 to 4carbon atoms, or a substituent of the following formula 3.

<Aspect 4>

The thickener according to any one of aspects 1 to 3, wherein theeasily-crystallizing hydrophobic monomer is a monomer of the followingformula 4:

where,

R⁵ is a straight-chain alkyl group of 16 to 22 carbon atoms, and

R⁶ is a hydrogen atom or a methyl group.

<Aspect 5>

The thickener according to any one of aspects 1 to 4, wherein thepoorly-crystallizing hydrophobic monomer is a monomer of the followingformula 5:

where,

R⁷ is a branched alkyl group of 18 or fewer carbon atoms, or astraight-chain alkyl group of 12 or fewer carbon atoms, and

R⁸ is a hydrogen atom or a methyl group.

<Aspect 6>

The thickener according to any one of aspects 3 to 5, wherein themonomer of formula 1 is at least one selected from among 2-hydroxyethyl(meth)acrylate, glyceryl (meth)acrylate, PPG-6 (meth)acrylate,2-hydroxypropyl (meth)acrylate, 2-hydroxy-2-methylpropyl (meth)acrylateand (meth)acrylic acid, and the monomer of formula 2 is at least oneselected from among N-(2-hydroxyethyl) (meth)acrylamide,N-isopropyl(meth)acrylamide and2-(meth)acrylamide-2-methylpropanesulfonic acid.

<Aspect 7>

The thickener according to any one of aspects 4 to 6, wherein themonomer of formula 4 is at least one selected from among cetyl(meth)acrylate, stearyl (meth)acrylate and behenyl (meth)acrylate.

<Aspect 8>

The thickener according to any one of aspects 5 to 7, wherein themonomer of formula 5 is at least one selected from among hexyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate,isooctyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate,lauryl (meth)acrylate and isostearyl (meth)acrylate.

<Aspect 9>

The thickener according to any one of aspects 1 to 8, wherein theoil-soluble copolymer contains the monomer unit of the hydrophilicmonomer in a range of 30 to 50 mol %, contains the monomer unit of theeasily-crystallizing hydrophobic monomer in a range of 40 to 65 mol %and contains the monomer unit of the poorly-crystallizing hydrophobicmonomer in a range of 5 to 15 mol %.

<Aspect 10>

The thickener according to any one of aspects 1 to 9, wherein the molarratio of the monomer unit of the easily-crystallizing hydrophobicmonomer and the monomer unit of the poorly-crystallizing hydrophobicmonomer in the oil-soluble copolymer is 5:1 to 8:1.

<Aspect 11>

The thickener according to any one of aspects 1 to 10, wherein theweight-average molecular weight of the oil-soluble copolymer is 9000 to80,000.

<Aspect 12>

An oil-based cosmetic containing a thickener according to any one ofaspects 1 to 11 and an oil.

<Aspect 13>

An oil-soluble copolymer having:

a monomer unit composed of at least one hydrophilic monomer selectedfrom among the following formula 1 and formula 2,

a monomer unit composed of an easily-crystallizing hydrophobic monomerof formula 4, and

a monomer unit composed of a poorly-crystallizing hydrophobic monomer offormula 5:

where,

R¹ is a hydrogen atom, a glyceryl group, a straight-chain or branchedhydroxyalkyl group of 1 to 4 carbon atoms, or a polypropyleneglycolgroup represented by —(C₃H₆O)_(n)H where n is an integer of 2 to 10, and

R² is a hydrogen atom or a methyl group,

where,

R³ is a hydrogen atom or a methyl group, and

R⁴ is a straight-chain or branched alkyl or hydroxyalkyl group of 1 to 4carbon atoms, or a substituent represented by the following formula 3:

where,

R⁵ is a straight-chain alkyl group of 16 to 22 carbon atoms, and

R⁶ is a hydrogen atom or a methyl group,

where,

R⁷ is a branched alkyl group of 18 or fewer carbon atoms, or astraight-chain alkyl group of 12 or fewer carbon atoms, and

R⁸ is a hydrogen atom or a methyl group.

Advantageous Effects of Invention

According to the invention, it is possible to provide a novel oilthickener that can impart a thickening effect for oils used incosmetics, and a novel oil-soluble copolymer that can be used as thethickener.

DESCRIPTION OF EMBODIMENTS

Embodiments of the invention will now be explained in detail. Theinvention is not limited to the embodiments described below, however,and various modifications may be implemented within the scope of thegist thereof.

The cosmetic oil thickener of the invention is an oil-soluble copolymerhaving a monomer unit composed of a hydrophilic monomer, a monomer unitcomposed of an easily-crystallizing hydrophobic monomer, and a monomerunit composed of a poorly-crystallizing hydrophobic monomer.

Without being limited to any particular principle, it is believed thatthe principle by which the oil-soluble copolymer described above acts toimpart a thickening effect by dissolution in oil is as follows.

The copolymer disclosed in PTL 3, for example, is composed of a specifichydrophobic monomer and a specific hydrophilic monomer. The hydrophobicmonomer provides the function of solubility in oils, while also beingeasily crystallizable. Therefore, crystallization takes place betweenthe copolymers by the hydrophobic monomer units as the copolymersapproach each other, so that a network structure incorporating the oilis formed. Presumably, a similar network structure is also formedbetween the copolymers due to hydrogen bonding of the hydrophilicmonomer units. As a result, the copolymers exhibit function as an oilygelling agent due to the two network structures. The gelatinouscomposition that has been gelled by the oily gelling agent, upondilution with an oil or the like, merely separates into the gelsubstance and oil, thus avoiding formation of a thick composition oflower viscosity than the gelatinous composition, for example.

The oil-soluble copolymer of the invention, on the other hand, has amonomer unit composed of a poorly-crystallizing hydrophobic monomer, inaddition to a monomer unit composed of a hydrophilic monomer and amonomer unit composed of an easily-crystallizing hydrophobic monomer.The poorly-crystallizing hydrophobic monomer unit inhibitscrystallization of the easily-crystallizing hydrophobic monomer unit,and reduces formation of the crystallized network structure among thetwo network structures, thus being able to function as an oil thickenerwithout gelation. While a copolymer composed of only a hydrophilicmonomer and a poorly-crystallizing hydrophobic monomer is either poorlysoluble or insoluble in oils, presumably the easily-crystallizinghydrophobic monomer unit composing the oil-soluble copolymer of theinvention contributes to its solubility in oils.

The definitions of terms used for the purpose of the invention are asfollows.

According to the invention, “hydrophilic monomer” means a monomer thatdissolves in water to an arbitrary degree, while “hydrophobic monomer”means other monomers, i.e. monomers that are essentially not misciblewith water.

The terms “easily-crystallizing hydrophobic monomer” and“poorly-crystallizing hydrophobic monomer” used for the invention referto the monomer that crystallizes relatively easily (easily-crystallizinghydrophobic monomer) and the monomer that crystallizes relatively poorly(poorly-crystallizing hydrophobic monomer), when the two hydrophobicmonomers are compared. Poorly-crystallizing hydrophobic monomers alsoinclude hydrophobic monomers that do not crystallize at all.

In other words, a hydrophobic monomer that crystallizes at hightemperature after it has cooled from a molten state may be considered tobe an “easily-crystallizing hydrophobic monomer”, while a hydrophobicmonomer that crystallizes at a lower temperature, or a hydrophobicmonomer that does not crystallize, after it has cooled from a moltenstate, may be considered to be a “poorly-crystallizing hydrophobicmonomer”. The crystallization temperature of the easily-crystallizinghydrophobic monomer may be defined as 20° C. or higher, 25° C. orhigher, or 30° C. or higher, for example, and the crystallizationtemperature of the poorly-crystallizing hydrophobic monomer may bedefined as 10° C. or lower, 5° C., or lower or 0° C. or lower, forexample.

The easily-crystallizing hydrophobic monomer may be a solid hydrophobicmonomer that crystallizes at ordinary temperature of 8 or more, 16 ormore, or 18 or more carbon atoms, and the poorly-crystallizinghydrophobic monomer may be a liquid hydrophobic monomer thatcrystallizes at ordinary temperature of 8 or more, 12 or more, or 16 ormore carbon atoms. For this purpose, “ordinary temperature” means atemperature range of 15° C. to 25° C.

The easily-crystallizing hydrophobic monomer may be a monomer having aglass transition temperature of 10° C. or higher, 12° C. or higher, or15° C. or higher, and 60° C. or lower, 55° C. or lower, or 50° C. orlower, for a homopolymer obtained using the monomer. Thepoorly-crystallizing hydrophobic monomer may be a monomer having a glasstransition temperature of −90° C. or higher, −88° C. or higher, or −86°C. or higher, and 0° C. or lower, −5° C. or lower, or −10° C. or lower,for a homopolymer obtained using the monomer.

The terms “gelation” and “gelatinous”, as used for the invention, can bedefined as viscosity with a shear rate of near 0 s⁻¹ without limit, forexample, static viscosity at a shear rate of 0.0001 s⁻¹ in a 25° C.atmosphere, and it may be defined as a range of higher than 20,000 Pa·s,25,000 Pa·s or higher, or 30,000 Pa·s or higher. The static viscosity ata shear rate of 0.0001 s⁻¹ in a 25° C. atmosphere for the thickenedmaterial that has been thickened with an oil thickener of the invention,may be defined as a range of 20,000 Pa·s or lower, 15,000 Pa·s or lower,or 10,000 Pa·s or lower, and it may be defined as a range of 100 Pa·s orhigher, 150 Pa·s or higher, or 200 Pa·s or higher.

The term “(meth)acrylic” according to the invention means “acrylic” or“methacrylic”.

<<Oil-Soluble Copolymer>>

The oil-soluble copolymer of the invention has a monomer unit composedof a hydrophilic monomer, a monomer unit composed of aneasily-crystallizing hydrophobic monomer, and a monomer unit composed ofa poorly-crystallizing hydrophobic monomer. Such a copolymer may beeither a random or block copolymer, but it is preferably random from theviewpoint of easier synthesis.

An oil-soluble copolymer may contain the monomer unit of the hydrophilicmonomer at 30 mol % or greater, 32 mol %, or greater or 35 mol % orgreater, and 50 mol % or less, 48 mol % or less or 45 mol % or less,from the viewpoint of the viscosity increase property; may contain themonomer unit of the easily-crystallizing hydrophobic monomer at 40 mol %or greater, 42 mol % or greater, or 45 mol % or greater, and 65 mol % orless, 63 mol % or less, 62 mol % or less, 61 mol % or less, or 60 mol %or less, from the viewpoint of solubility in oils; and may contain themonomer unit of the poorly-crystallizing hydrophobic monomer at 5 mol %or greater, 8 mol % or greater, or 9 mol % or greater, and 15 mol % orless, 13 mol % or less, or 12 mol % or less, from the viewpoint ofcrystallization inhibition.

In order to inhibit gelation during crystallization by the monomer unitof the easily-crystallizing hydrophobic monomer, and to more easilyexhibit the viscosity increase property, the molar ratio of the monomerunit of the easily-crystallizing hydrophobic monomer and the monomerunit of the poorly-crystallizing hydrophobic monomer is preferably inthe range of 5:1 to 8:1, more preferably in the range of 5:1 to 7:1 andeven more preferably in the range of 5.5:1 to 6:1.

The molecular weight of the oil-soluble copolymer is not particularlyrestricted, and for example, it may be in the range of 9,000 to 80,000,preferably in the range of 20,000 to 50,000 and more preferably in therange of 25,000 to 40,000, as the weight-average molecular weight basedon polystyrene using gel permeation chromatography.

<Hydrophilic Monomer>

Examples of hydrophilic monomers to be used include one or more monomersselected from among formula 1 and formula 2 below.

In formula 1, R¹ is a hydrogen atom, a glyceryl group, a straight-chainor branched hydroxyalkyl group of 1 to 4 carbon atoms, or apolypropyleneglycol group represented by —(C₃H₆O)_(n)H wherein n is aninteger of 2 to 10, and R² is a hydrogen atom or a methyl group.Examples of hydroxyalkyl groups include 2-hydroxyethyl, 2-hydroxypropyl,2-hydroxyethyl-2-methylpropyl, 2-hydroxybutyl, 3-hydroxybutyl and4-hydroxybutyl groups.

Specific examples of hydrophilic monomers represented by formula 1include 2-hydroxyethyl (meth)acrylate, glyceryl (meth)acrylate, PPG-6(meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxy-2-methylpropyl(meth)acrylate and (meth)acrylic acid, among which glyceryl(meth)acrylate, 2-hydroxyethyl (meth)acrylate and (meth)acrylic acid arepreferred, and glyceryl methacrylate, 2-hydroxyethyl acrylate andacrylic acid are more preferred.

In formula 2, R³ is a hydrogen atom or a methyl group, and R⁴ is astraight-chain or branched alkyl or hydroxyalkyl group of 1 to 4 carbonatoms, or a substituent of the following formula 3.

Examples of alkyl groups for R⁴ in this formula include ethyl, propyl,isopropyl and butyl groups, and examples of hydroxyalkyl groups include2-hydroxyethyl, 2-hydroxypropyl, 2-hydroxyethyl-2-methylpropyl,2-hydroxybutyl, 3-hydroxybutyl and 4-hydroxybutyl groups.

Specific examples of hydrophilic monomers represented by formula 2include N-(2-hydroxyethyl) (meth)acrylamide, N-isopropyl(meth)acrylamideand 2-(meth)acrylamide-2-methylpropanesulfonic acid. Preferred amongthese are N-(2-hydroxyethyl) (meth)acrylamide andN-isopropyl(meth)acrylamide, with N-(2-hydroxyethyl) (meth)acrylamidebeing more preferred and N-(2-hydroxyethyl)acrylamide being especiallypreferred.

<Easily-Crystallizing Hydrophobic Monomer>

In formula 4, R⁵ is a straight-chain alkyl group of 16 to 22 carbonatoms, and R⁶ is a hydrogen atom or a methyl group. Examples ofstraight-chain alkyl groups of 16 to 22 carbon atoms include cetyl,stearyl and behenyl groups.

Such a hydrophobic monomer is an alkyl (meth)acrylate, or in other wordsan ester of (meth)acrylic acid and an alcohol having a straight-chainalkyl group of 16 to 22 carbon atoms. Specific examples include cetyl(meth)acrylate, stearyl (meth)acrylate, and behenyl (meth)acrylate,among which stearyl (meth)acrylate is preferred.

<Poorly-Crystallizing Hydrophobic Monomer>

In formula 5, R⁷ is a branched alkyl group of 18 or fewer carbon atoms,or a straight-chain alkyl group of 12 or fewer carbon atoms, and R⁸ is ahydrogen atom or a methyl group. Straight-chain or branched alkyl groupsto be used for R⁷ include alkyl groups of 3 or more, 4 or more, 5 ormore, 6 or more, 7 or more, or 8 or more carbon atoms. R⁸ is preferablya hydrogen atom.

Specific examples of hydrophobic monomers represented by formula 5include hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl(meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, isodecyl(meth)acrylate, lauryl (meth)acrylate, and isostearyl (meth)acrylate,among which 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, lauryl(meth)acrylate, and isostearyl (meth)acrylate are preferred, octyl(meth)acrylate, lauryl (meth)acrylate, isostearyl (meth)acrylate aremore preferred, and octyl (meth)acrylate and isostearyl (meth)acrylateare even more preferred.

<Optional Monomers>

The oil-soluble copolymer of the invention may also have a monomer unitcomposed of a monomer other than those of formulas 1, 2, 4 and 5, withina range that does not interfere with the effect of the invention. Theproportion of the monomer unit may be in the range of 30 mol % or less,20 mol % or less, 10 mol % or less, or 5 mol % or less of the totalconstituent monomer units. Examples of such monomers include one or moremonomers selected from the group consisting of anionic monomers,cationic monomers, nonionic monomers, and other monomers.

<Method for Producing Oil-Soluble Copolymer>

The oil-soluble copolymer of the invention can be obtained by a knownpolymerization method, such as charging a mixture of the hydrophilicmonomer, easily-crystallizing hydrophobic monomer andpoorly-crystallizing hydrophobic monomer, a polymerization solvent and apolymerization initiator into a reactor, and conducting polymerizationreaction for several hours while heating to maintain a constanttemperature, with no particular limitation to this method. Thepolymerization solvent may then be distilled off from the solution inthe reactor to obtain the oil-soluble copolymer.

A copolymer can also be obtained by a living radical polymerizationprocess. This will facilitate adjustment of the molecular weight of thecopolymer, allowing a copolymer with a more narrow molecular weightdistribution to be produced.

(Polymerization Solvent)

The polymerization solvent may be appropriately selected as a solventthat does not exhibit reactivity with the functional groups of themonomers. Examples include, but are not limited to, hydrocarbon-basedsolvents such as n-hexane, n-octane, n-decane, isodecane, cyclohexane,methylcyclohexane, toluene, xylene, ethylbenzene and cumene;alcohol-based solvents such as methanol, ethanol, n-propanol,isopropanol, n-butanol, isobutanol, n-hexanol, benzyl alcohol andcyclohexanol; hydroxyl-containing glycol ethers such as ethylene glycol,diethylene glycol, propylene glycol, dipropylene glycol,methylcellosolve, ethylcellosolve, butylcellosolve, propyleneglycolmonomethyl ether, propyleneglycol monoethyl ether, propyleneglycolpropyl ether, butylcarbitol, butyltriethylene glycol andmethyldipropylene glycol; glycol-based solvents such as diglyme,triglyme, methylcellosolve acetate, propyleneglycol monomethyl etheracetate, dipropyleneglycol butyl ether acetate and diethyleneglycolmonobutyl ether acetate; ether-based solvents such as diethyl ether,dipropyl ether, methylcyclopropyl ether, tetrahydrofuran, dioxane andanisole; ketone-based solvents such as dimethyl ketone, diethyl ketone,ethyl methyl ketone, isobutylmethyl ketone, cyclohexanone, isophoroneand acetophenone; ester-based solvents such as methyl acetate, ethylacetate, butyl acetate, propyl acetate, methyl butyrate, ethyl butyrate,caprolactone, methyl lactate and ethyl lactate; halogen-based solventssuch as chloroform, dichloromethane, dichloroethane ando-dichlorobenzene; amide-based solvents such as formamide,N,N-dimethylformamide, N,N-dimethylacetamide, 2-pyrrolidone,N-methyl-2-pyrrolidone and ε-caprolactam; and dimethyl sulfoxide,sulfolane, tetramethylurea, ethylene carbonate, propylene carbonate,dimethyl carbonate, diethyl carbonate, nitromethane, acetonitrile,nitrobenzene and dioctyl phthalate.

(Polymerization Initiator)

The polymerization initiator used may be a conventionally known one, andexamples include but are not particularly limited to organic peroxidesand azo compounds. Specifically, these include benzoyl peroxide, dicumylperoxide, diisopropyl peroxide, di-t-butyl peroxide, t-butylperoxybenzoate, t-hexyl peroxybenzoate, t-butylperoxy-2-ethyl hexanoate,t-hexylperoxy-2-ethyl hexanoate,1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane,2,5-dimethyl-2,5-bis(t-butylperoxy)hexyl-3,3-isopropyl hydroperoxide,t-butyl hydroperoxide, dicumyl hydroperoxide, acetyl peroxide,bis(4-t-butylcyclohexyl)peroxy dicarbonate, isobutyl peroxide,3,3,5-trimethylhexanoyl peroxide, lauryl peroxide,1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane,1,1-bis(t-hexylperoxy)3,3,5-trimethylcyclohexane,2,2′-azobis(isobutyronitrile), 2,2′-azobis(2,4-dimethylvaleronitrile),2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) and dimethyl2,2′-azobis(isobutyrate).

(Polymerization Time)

The time that the state of reflux is maintained, i.e. the polymerizationtime, is preferably long enough until the monomers disappear, and it maybe, but is not limited to, 1 hour or longer, 2 hours or longer or 3hours or longer, and 144 hours or shorter, 72 hours or shorter or 48hours or shorter, for example.

(Polymerization Atmosphere)

The polymerization atmosphere is not particularly limited, and thepolymerization may be in an air atmosphere, i.e. with a normalconcentration of oxygen in the polymerization system, or if necessary itmay be carried out in an inert gas atmosphere such as nitrogen or argonto remove the oxygen. Each of the materials used may have the impuritiesremoved by distillation, or with active carbon or alumina, or acommercial product may be used directly. The polymerization may beconducted under shielding from light, or in a transparent container suchas glass.

(Other Components Contributing to Polymerization Reaction)

Other components such as chain transfer agents may be added to thereactor as necessary for molecular weight modification of the copolymer,for example. Examples of chain transfer agents include, but are notparticularly limited to, compounds with mercapto groups such aslaurylmercaptane and thioglycerol; inorganic salts such as sodiumhypophosphite and sodium hydrogen sulfite; and a-methyl styrene dimer.The amount of chain transfer agent used is determined as appropriate forthe molecular weight range desired for the copolymer, but it is usuallypreferred to be in the range of 0.01 to 10 mass % with respect to themonomers.

<<Usage of Oil-Soluble Copolymer>>

The oil-soluble copolymer of the invention may be used for variouspurposes such as cosmetics, paints, inks and coating compositions, sinceit can be dissolved in different hydrophobic organic solvents thatcontain oils, thereby increasing the viscosity of such solvents. It ispreferably used as an oil thickener for a cosmetic. A hydrophobicorganic solvent, for this purpose, is a solvent that at least partiallyseparates when mixed with water.

The composition that includes the oil-soluble copolymer of the inventioncan also be prepared as a highly transparent composition. This willallow the composition to exhibit a viscosity increase property withoutaltering the tint of the hydrophobic organic solvent.

From the viewpoint of the viscosity increase property and stability, theamount of oil-soluble copolymer of the invention added may be 1 mass %or greater, 2 mass % or greater, or 3 mass % or greater, and 10 mass %or lower, 8 mass % or lower or 5 mass % or lower, in 100 mass % of themixture of the copolymer and hydrophobic organic solvent.

The method of preparing the composition containing the copolymer andhydrophobic organic solvent is not particularly restricted, and forexample, preferably the copolymer and hydrophobic organic solvent aremixed after both are dissolved, with heating as necessary during thedissolution and mixing.

The oil-soluble copolymer of the invention will now be describedassuming its use as an oil thickener in a cosmetic, though this is notlimitative on the invention.

<Cosmetic> (Hydrophobic Organic Solvent)

When the oil-soluble copolymer of the invention is to be used as acosmetic oil thickener, hydrophobic organic solvents may be used aloneor in combination of two or more, and it is preferred to use one or moreof various oils, and especially oils that are compatible withthickeners, such as hydrocarbon oils, ester oils, or higher alcohols,for example, with no limitation to these.

Hydrocarbon oils include liquid paraffin, tetraisobutane, hydrogenatedpolydecene, olefin oligomers, isododecane, isohexadecane, squalane andhydrogenated polyisobutene.

Ester oils include cetyl isooctanoate (cetyl 2-ethylhexanoate),triethylhexanoin, 2-ethylhexyl palmitate, neopentyl glycol dicaprate,triisostearin, diisostearyl malate, PPG-3 dipivalate, di-2-ethylhexylsuccinate, 2-ethylhexyl 2-ethylhexanoate, polyglyceryl-6 octacaprylateand (caprylic/capric) triglyceride.

Higher alcohols include isostearyl alcohol and oleyl alcohol.

The total amount of hydrocarbon oils, ester oils and higher alcohols ispreferably 80 mass % or greater and more preferably 85 mass % or greaterin the oil.

The oil thickener of the invention can be suitably used in variouscosmetics, and especially oily cosmetics or water-in-oil type emulsifiedcosmetics.

(Oily Cosmetics)

Examples of oily cosmetics include skin care cosmetics such as sunprotection oils and beauty essences; makeup cosmetics such as lipstick,gloss, mascara and mascara foundations; skin cleansers such as makeupremovers; and hair cosmetics such as hair oils and hair treatments.

(Water-in-Oil Type Emulsified Cosmetics)

Examples of water-in-oil emulsified cosmetics include skin carecosmetics such as milky lotions creams, face oils, body oils and beautyessences; makeup cosmetics such as foundations, cosmetic bases,lipstick, rouge, eye-shadow, mascara and mascara foundations; skincleansers such as makeup removers; hair cleansers; hair cosmetics suchas hair treatments and hair oils; sunscreen cosmetics; and hair dyes.

(Optional Components)

The cosmetic of the invention may also contain other components asappropriate in ranges that do not interfere with the effect of theinvention. Such components include additives that can generally be addedto cosmetics, examples of which are anionic surfactants, cationicsurfactants, amphoteric surfactants, nonionic surfactants, humectants,water-soluble polymers, film-forming agents such as silicone modifiedpolysaccharides, metal ion sequestering agents, lower alcohols,polyhydric alcohols, various extracts, sugars, amino acids, organicamines, polymer emulsions, chelating agents, ultraviolet absorbers, pHadjustors, skin nutrients, vitamins, drugs, quasi drugs, water-solubledrugs that are suitable for use in cosmetics, antioxidants, bufferingagents, antiseptic agents, antioxidant aids, propellants, organic systempowders, pigments, dyes, coloring agents, perfumes, water, acidcomponents and alkali components. Such optional components may be addedas appropriate to the oil phase, or to the aqueous phase when present.

EXAMPLES

The invention will now be described in greater detail by examples, withthe understanding that they are not restrictive on the invention.

Examples 1 to 29 and Comparative Examples 1 and 2 <Synthesis ofCopolymer>

In a 1 liter-volume four-necked flask equipped with a reflux condenser,thermometer, nitrogen gas inlet tube and stirrer, there were charged 250parts by mass of ethanol, and a total of 100 parts by mass of a mixtureof the monomers listed in Table 1 or Table 2 in the listed monomer molarratios, and the mixture was heated under a nitrogen stream. When themixture reached a state of reflux at approximately 80° C., 1 part bymass of 2,2′-azobisisobutyronitrile was added, and the reflux state wasmaintained for 4 hours for polymerization reaction. The ethanol solventwas then distilled off from the solution in the flask to obtain acopolymer. For Examples 12 to 18, however, the charging amounts of theethanol and 2,2′-azobisisobutyronitrile were adjusted as appropriate forthe prescribed weight-average molecular weights.

(Weight-Average Molecular Weight)

The weight-average molecular weight of the obtained copolymer wascalculated from gel permeation chromatography under the followingmeasuring conditions.

Apparatus: Prominence HPLC system (product of Shimadzu Corp.)

Column: Shodex KF-805, KF-803, KF-801 (series) (product of Showa DenkoK.K.)

Mobile phase: Tetrahydrofuran

Flow rate: 1 mL/min

Detector: Differential refractometer

Temperature: 40° C.

Molecular weight reference sample: Polystyrene

<Evaluation Methods>

(Evaluation of Compatibility with Oils)

The copolymer was mixed with different oils, and the compatibility ofthe copolymer with the oils when dissolved at 85° C. while stirring wasvisually observed and evaluated on the following scale, giving theresults shown in Table 1. The copolymer content was adjusted to 3 mass %of the copolymer with respect to the total amount of the copolymer andoil.

A: Easily dissolved, compatible.

B: Difficult to dissolve, but compatible.

C: Slight precipitation observed.

D: Notable precipitation observed.

E: Completely incompatible.

(Evaluation of Viscosity Increase Property)

The copolymer was mixed with different oils, and each mixture wasdissolved at 85° C. while stirring and then cooled to room temperatureto prepare a sample. The viscosity increase property was evaluated usingan MCR302 rheometer by Anton Paar, under conditions of 25° C., 1atmosphere, on the following scale, based on the viscosity with a shearrate of near 0 s⁻¹ without limit, i.e. a shear rate of 0.0001 s⁻¹. Theresults are shown in Table 1. The copolymer content was adjusted to 3mass % of the copolymer with respect to the total amount of thecopolymer and oil.

A: ≥2000 Pa·s, ≤20,000 Pa·s

B: ≥1000 Pa·s, <2000 Pa·s

C: ≥100 Pa·s, <1000 Pa·s

D: ≥1 Pa·s, <100 Pa·s

E: >20,000 Pa·s (gelled)

(Transparency Evaluation)

The copolymer was mixed with different oils, and each mixture wasdissolved at 85° C. while stirring and then cooled to room temperatureto prepare a sample. The transparency of the sample was visuallyobserved and evaluated on the following scale, giving the results shownin Table 1. The copolymer content was adjusted to 3 mass % of thecopolymer with respect to the total amount of the copolymer and oil.

A: Excellent transparency exhibited.

B: Satisfactory transparency exhibited.

C: Slight turbidity exhibited.

D: Notable opacity.

E: Opaque.

TABLE 1 Example 1 2 3 4 5 6 7 8 9 10 11 12 13 Monomer GLM 40 40 40 40 4040 40 40 40 40 40 40 40 (mol %) SA 52 51 50 52 51 50 51 51 52 51 50 5151 BEA — — — — — — — — — — — — — 2EHA 8 9 10 — — — — — — — — — — LMA — —— 8 9 10 9 9 — — — — — ISA — — — — — — — — 8 9 10 9 9 NOA — — — — — — —— — — — — — Weight-average 55400 50,000 44100 75200 75200 77900 3090034800 59200 51200 48900 9300 16300 molecular weight HPD Compat- B C D BB B A A B B B A A ibility Viscosity A A B A A B C C A A B A A increaseproperty Transparency E D C C C C C C B B B B B CIO Compat- B B C B B BA A B B B A A ibility Viscosity B B B C C C D D A A B A A increaseproperty Transparency E D C C C D C C B B B B B Example Comp. Ex. 14 1516 17 18 19 20 21 1 2 Monomer GLM 40 40 40 40 40 40 40 40 40 40 (mol %)SA 51 51 51 51 51 51 51 51 — — BEA — — — — — — — — 60 — 2EHA — — — — — —— — — — LMA — — — — — — — — — — ISA 9 9 9 9 9 — — — — 60 NOA — — — — — 99 9 — — Weight-average 23,000 34200 39500 43200 60500 19700 41800 5790029300 23500 molecular weight HPD Compat- A A A B D A A B A E ibilityViscosity A A A A A A A A E — increase property Transparency B B B B B BB B E — CIO Compat- A A A A B A A B A E ibility Viscosity A A A A A A AA E — increase property Transparency B B B B B B B B E — GLM: Glycerylmethacrylate of hydrophilic monomer (melting point: −40° C., homopolymerglass transition temperature: 55° C.). SA: Stearyl acrylate ofeasily-crystallizing hydrophobic monomer (melting point: 28° C.,homopolymer glass transition temperature: 35° C.). BEA: Behenyl acrylateof easily-crystallizing hydrophobic monomer (melting point: 46° C.,homopolymer glass transition temperature: 50° C.). 2EHA: 2-Ethylhexylacrylate of poorly-crystallizing hydrophobic monomer (melting point:−90° C. homopolymer glass transition temperature: −85° C.). LMA: Laurylmethacrylate of poorly-crystallizing hydrophobic monomer (melting point:−23° C., homopolymer glass transition temperature: −65° C.). ISA:Isostearyl acrylate of poorly-crystallizing hydrophobic monomer (meltingpoint: <−50° C., homopolymer glass transition temperature: −18° C.).NOA: n-Octyl acrylate of poorly-crystallizing hydrophobic monomer(melting point: <−50° C., homopolymer glass transition temperature: −65°C.). HPD: Hydrogenated polydecene of oil. Static viscosity at 25° C.:0.03 Pa · s. CIO: Cetyl isooctanoate of oil. Static viscosity at 25° C.:0.01 Pa · s.

TABLE 2 Example 15 22 23 24 25 26 27 28 29 Monomer GLM 40 — — — — — — —— (mol %) HEAA — 40 — — — — — — — HEA — — 40 — — — — — — Aa — — — 40 — —— — — HBMA — — — — 40 — — — — NIPAM — — — — — 40 — — — HPMA — — — — — —40 — — HEMA — — — — — — — 40 — AP-400 — — — — — — — — 40 SA 51 51 51 5151 51 51 51 51 ISA 9 9 9 9 9 9 9 9 9 Weight-average 34200 30500 27,00033,000 37500 36700 33900 38500 29300 molecular weight HPD Compat- A A AA D A D A A ibility Viscosity A A A A C B C B C increase propertyTransparency B B B B C C C C C GLM: Glyceryl methacrylate of hydrophilicmonomer. HEAA: 2-Hydroxyethylacrylamide of hydrophilic monomer. HEA:2-Hydroxyethyl acrylate of hydrophilic monomer. Aa: Acrylic acid ofhydrophilic monomer HBMA: 2-Hydroxy-2-methylpropyl methacrylate ofhydrophilic monomer. NIPAM: N-Isopropylacrylamide of hydrophilicmonomer. HPMA: 2-Hydroxypropyl methacrylate of hydrophilic monomer.HEMA: 2-Hydroxyethyl methacrylate of hydrophilic monomer. AP-400: PPG-6acrylate of hydrophilic monomer. SA: Stearyl acrylate ofeasily-crystallizing hydrophobic monomer ISA: Isostearyl acrylate ofpoorly-crystallizing hydrophobic monomer HPD: Hydrogenated polydecene ofoil.

<Results>

As clearly seen from Table 1, with the composition of ComparativeExample 1 which used a copolymer that did not include a monomer unitcomposed of a poorly-crystallizing hydrophobic monomer, the copolymerwas compatible with oils but the composition itself gelled. With thecomposition of Comparative Example 2 which used a copolymer that did notinclude a monomer unit composed of an easily-crystallizing hydrophobicmonomer, the copolymer was not compatible with oils. With thecompositions of Examples 1 to 21 which used copolymers of the inventionthat included both monomer units, it was confirmed that the copolymerswere compatible with oils, and were able to increase viscosity withoutgelling with at least one of the oils.

Upon comparing Examples 1 to 3 which used 2-ethylhexyl acrylate,Examples 4 to 6 which used lauryl methacrylate, Examples 9 to 11 whichused isostearyl acrylate and Examples 19 to 21 which used n-octylacrylate as the poorly-crystallizing hydrophobic monomer, it was foundthat using lauryl methacrylate, isostearyl acrylate or n-octyl acrylatefurther improved performance including transparency.

As clearly seen from Table 2, it was confirmed that the copolymers ofthe invention were able to increase viscosity without gelling of oils,even when using a hydrophilic monomer other than glyceryl methacrylate.

Upon comparing Example 25 which used 2-hydroxy-2-methylpropylmethacrylate and Example 27 which used 2-hydroxypropyl methacrylate,with Example 26 which used N-isopropylacrylamide and Example 28 whichused 2-hydroxyethyl methacrylate as the hydrophilic monomer, it wasfound that Examples 26 and 28 had further improved compatibility andviscosity increase properties. With Example 15 which used glycerylmethacrylate, Example 22 which used 2-hydroxyethylacrylamide, Example 23which used 2-hydroxyethyl acrylate and Example 24 which used acrylicacid, it was found that the compatibility, viscosity increase propertiesand transparency were further improved.

1. A cosmetic oil thickener which is an oil-soluble copolymer having amonomer unit composed of a hydrophilic monomer, a monomer unit composedof an easily-crystallizing hydrophobic monomer, and a monomer unitcomposed of a poorly-crystallizing hydrophobic monomer.
 2. The thickeneraccording to claim 1, wherein the easily-crystallizing hydrophobicmonomer is a monomer of 8 or more carbon atoms that is a solid atordinary temperature, and the poorly-crystallizing hydrophobic monomeris a monomer of 8 or more carbon atoms that is a liquid at ordinarytemperature.
 3. The thickener according to claim 1, wherein thehydrophilic monomer is at least one monomer selected from among thefollowing formula 1 and formula 2:

where, R¹ is a hydrogen atom, a glyceryl group, a straight-chain orbranched hydroxyalkyl group of 1 to 4 carbon atoms, or apolypropyleneglycol group represented by —(C₃H₆O)_(n)H where n is aninteger of 2 to 10, and R² is a hydrogen atom or a methyl group,

where, R³ is a hydrogen atom or a methyl group, and R⁴ is astraight-chain or branched alkyl or hydroxyalkyl group of 1 to 4 carbonatoms, or a substituent of the following formula 3:


4. The thickener according to claim 1, wherein the easily-crystallizinghydrophobic monomer is a monomer of the following formula 4:

where, R⁵ is a straight-chain alkyl group of 16 to 22 carbon atoms, andR⁶ is a hydrogen atom or a methyl group.
 5. The thickener according toclaim 1, wherein the poorly-crystallizing hydrophobic monomer is amonomer of the following formula 5:

where, R⁷ is a branched alkyl group of 18 or fewer carbon atoms, or astraight-chain alkyl group of 12 or fewer carbon atoms, and R⁸ is ahydrogen atom or a methyl group.
 6. The thickener according to claim 3,wherein the monomer of formula 1 is at least one selected from among2-hydroxyethyl (meth)acrylate, glyceryl (meth)acrylate, PPG-6(meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxy-2-methylpropyl(meth)acrylate and (meth)acrylic acid, and the monomer of formula 2 isat least one selected from among N-(2-hydroxyethyl) (meth)acrylamide,N-isopropyl(meth)acrylamide and2-(meth)acrylamide-2-methylpropanesulfonic acid.
 7. The thickeneraccording to claim 4, wherein the monomer of formula 4 is at least oneselected from among cetyl (meth)acrylate, stearyl (meth)acrylate andbehenyl (meth)acrylate.
 8. The thickener according to claim 5, whereinthe monomer of formula 5 is at least one selected from among hexyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate,isooctyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate,lauryl (meth)acrylate and isostearyl (meth)acrylate.
 9. The thickeneraccording to claim 1, wherein the oil-soluble copolymer contains themonomer unit of the hydrophilic monomer in a range of 30 to 50 mol %,contains the monomer unit of the easily-crystallizing hydrophobicmonomer in a range of 40 to 65 mol % and contains the monomer unit ofthe poorly-crystallizing hydrophobic monomer in a range of 5 to 15 mol%.
 10. The thickener according to claim 1, wherein the molar ratio ofthe monomer unit of the easily-crystallizing hydrophobic monomer and themonomer unit of the poorly-crystallizing hydrophobic monomer in theoil-soluble copolymer is 5:1 to 8:1.
 11. The thickener according toclaim 1, wherein the weight-average molecular weight of the oil-solublecopolymer is 9000 to 80,000.
 12. An oil-based cosmetic containing athickener according to claim 1 and an oil.
 13. An oil-soluble copolymerhaving: a monomer unit composed of at least one hydrophilic monomerselected from among the following formula 1 and formula 2, a monomerunit composed of an easily-crystallizing hydrophobic monomer of formula4, and a monomer unit composed of a poorly-crystallizing hydrophobicmonomer of formula wherein formulas 1, 2, 4, and 5 are as follows:

where, R¹ is a hydrogen atom, a glyceryl group, a straight-chain orbranched hydroxyalkyl group of 1 to 4 carbon atoms, or apolypropyleneglycol group represented by —(C₃H₆O)_(n)H where n is aninteger of 2 to 10, and R² is a hydrogen atom or a methyl group,

where, R³ is a hydrogen atom or a methyl group, and R⁴ is astraight-chain or branched alkyl or hydroxyalkyl group of 1 to 4 carbonatoms, or a substituent represented by the following formula 3:

where, R⁵ is a straight-chain alkyl group of 16 to 22 carbon atoms, andR⁶ is a hydrogen atom or a methyl group,

where, R⁷ is a branched alkyl group of 18 or fewer carbon atoms, or astraight-chain alkyl group of 12 or fewer carbon atoms, and R⁸ is ahydrogen atom or a methyl group.